1. Field of the Invention
The present invention relates to a polishing pad. More specifically, it relates to a polishing pad which has good slurry retainability, a high degree of hardness, and excellent polishing properties such as a capability of forming a polished surface with sufficient planarity.
The polishing pad of the present invention is widely used for polishing the surfaces of semiconductor wafers and other materials.
2. Description of the Prior Art
As a polishing method capable of forming a polished surface with a high degree of planarity, CMP (Chemical Mechanical Polishing) has been drawing attention in recent years. In CMP, a surface to be polished is polished by sliding or rotating a polishing pad and the surface against each other with a slurry which is a water-based dispersion having abrasives dispersed therein caused to flow down on the surface of the polishing pad.
One of factors which significantly affect productivity in this CMP is a polishing rate. This polishing rate can be significantly improved by increasing the amount of a retained slurry from a conventional amount.
In CMP, heretofore, a polyurethane foam containing fine air bubbles is used as the polishing pad, and polishing is carried out with a slurry retained in pores opened on a surface of this polishing pad.
However, it is difficult to control the degree of foaming in the polyurethane foam to a desired degree, and it is very difficult to control the sizes of the air bubbles, a foaming density and other properties uniformly throughout the foam. Consequently, the quality of the polishing pad comprising the polyurethane foam varies, thereby causing a variation in the polishing rate and other properties.
JP-A 8-500622, JP-A 2000-34416 and JP-A 2000-33552 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) disclose various resins having water-soluble materials dispersed therein as polishing pads whose pores can be controlled more easily than the above polishing pad comprising the foam. Of these publications, the former two publications describe the effectiveness of a polishing pad containing a water-soluble material. Further, in the last publication, a material of a matrix material is studied, and a polishing pad for which more stable polishing and an improvement in polishing rate are recognized is disclosed. However, the slurry retainability and polishing rate of the polishing pad are not necessarily satisfactory.
Furthermore, slurries having different pHs in a wide range of pHs have heretofore been used, and a polishing pad capable of adapting to these various slurries different in pH has been desired.